This invention relates to novel conductive elastomers having low electrical resistivity and very good physical properties.
Conductive elastomers are known to the art. They are made by compounding the elastomer with a conductive filler, for example, with graphite, carbon black, or powdered metal. A number of conductive elastomer types have been reported, including those based on polymers of chloroprene or of unsaturated hydrocarbon monomers, chlorosulfonated polyethylene, and fluoroelastomers. Some of these materials found use in moderate temperature heating elements, ignition wires, and conductive coatings. The best commercial materials had a rather high resistivity of about 6 ohm.cm. If the proportion of conductive filler was increased, the physical properties of the polymer deteriorated rapidly. Certain fluoroelastomers could be compounded to low-resistivity conductive materials, but their physical properties were quite poor. There was no known conductive elastomer that could be cast or fabricated into a very thin self-supporting film or tape for use in electronic equipment, especially where good strength, flexibility, and aging properties are important. Furthermore, it was necessary in preparing many prior art conductive elastomer compositions to observe a strict blending schedule because the conductivities of those compositions were dependent on the blending time. Once the highest conductivity composition was obtained, usually as soon as all the carbon was dispersed, further blending resulted in a conductivity decrease. Finally, many of those prior art conductive elastomers had poor aging characteristics.
It thus is highly desirable to provide an elastomeric composition having high conductivity, good physical properties, and good aging characteristics, capable of being cast or fabricated into very thin films, sheets, or tapes.